Consider the following statements: In a nuclear reactor, self-sustained chain reaction is possible, because 1. more neutrons are released in each of the fission reactions. 2. the neutrons immediately take part in the fission process. 3. the fast neutrons are slowed down by Graphite. 4. every neutron released in the fission reaction initiates further fission. Which of these statements are correct?

1. Statement 1: In nuclear fission, a heavy nucleus splits, releasing energy and typically 2-3 neutrons. This release of more neutrons than consumed (one neutron initiates fission) makes a chain reaction possible. (Correct) 2. Statement 2: The released neutrons are initially fast and need to be slowed down (moderated) to efficiently cause further fission in fissile materials like Uranium-235. They do not immediately take part effectively. (Incorrect) 3. Statement 3: Materials like Graphite or heavy water are used as moderators in a nuclear reactor to slow down fast neutrons. (Correct) 4. Statement 4: Not every neutron released initiates further fission. Some may escape the reactor core, or be absorbed by non-fissile materials or control rods. (Incorrect) 5. Therefore, statements 1 and 3 are correct.